1. Field of the Invention
This invention relates generally to a method and structure for producing a Z-axis interconnection of printed wiring board and chip carrier elements and, more particularly, to a method of providing a printed wiring board or chip carrier formed of a plurality of elements which are laminated together to form a printed wiring board or chip carrier having Z-axis interconnections.
2. Background of the Invention
Printed wiring boards and chip carriers are conventionally made up of a plurality of individual elements joined together to provide various levels of wiring on the surfaces of the elements and interconnections between the various wiring levels, such interconnection between the various levels often being referred to as Z-axis interconnections. In some conventional techniques for forming such interconnections in the Z-axis, a drilling operation is required after the various elements have been joined together. This requires precise alignment of all of the elements, as well as precise drilling of the final structure, which creates the possibility of misalignment, at least requiring either rework of the board or, at most, scrapping of the board after it reaches this late assembly stage. Moreover, the z-interconnection provides a more efficient utilization of space on the circuit board compared to conventional through hole drilling. Thus, it is desirable to provide elements for forming a printed wiring board or chip carrier and a technique for forming the elements in the printed wiring board or chip carrier which does not require drilling in the final stage but, rather, allows the individual elements to be formed with the components of the Z-axis connection which, when finally joined together, will provide the necessary connection between various layers of metal wiring.
According to the present invention, a method of forming a member for a composite wiring board or chip carrier and a method of forming the composite wiring board or chip carrier, as well as the member of the composite wiring board or chip carrier, are provided. The member is formed by providing a dielectric substrate having opposite faces and optionally forming an electrically conductive coating on at least one face thereof, preferably by laminating copper on the at least one face. At least one electrical conductive coating, if provided, is circuitized, preferably at this stage, but later if desired. At least one layer of adhesive film or tape is applied over at least one face. At least one opening is formed through the substrate extending from one face to the other and through each conductive coating, if present, and through each layer of adhesive film or tape. Openings to form one or more blind vias may also be formed. An electrically conductive material is dispensed in each of the openings, including through the openings in the adhesive film or tape. The conductive material is then partially cured. Alternately, a solder paste could be deposited in the holes and then reflowed in an oven. Each layer of adhesive film or tape is then removed to allow a nub of the conductive material to extend above the substrate face, and any remaining conductive material, if any, to thereby form a member that can be electrically joined face-to-face with another member or other circuitized structure. In one embodiment, another member is then formed in a similar manner and the two members joined face-to-face to provide a printed wiring board with electrical interconnections in the Z-axis, i.e. between the circuit traces on opposite faces of the circuit board so formed. In another embodiment, the member is used to join with at least one other circuitized member. The invention also contemplates a member formed according to this invention and a printed wiring board formed using at least one member, either as a circuitized member or as a joining member.